Project Summary Melanoma is a devastating disease, with five-year survival rates for metastatic disease under 15%. Exciting new therapies have emerged for BRAF-mutant melanoma, but NRAS mutant melanoma continues to have poor prognosis and limited therapeutic options. Even with the newest targeted and immunotherapy, a large percent of patients does not benefit and/or experience disease progression. In particular, the ~30% of mela- noma patients whose tumors have mutations in the NRAS oncogene, and those who become resistant to cur- rent therapies, have limited treatment options and poor prognosis. Developing effective therapies for NRAS mutant melanoma and overcoming resistance to BRAF/MEK inhibition is of outmost importance in melanoma. Identifying vulnerabilities in NRAS-driven melanomas is critical to design effective treatments for this class of tumors, as there are currently no drugs to directly inhibit mutant NRAS. Mutations in the TERT promoter, (the catalytic subunit of Telomerase) are found in approximately 70% of melanomas, constituting the most frequent genetic alteration in this cancer. Preliminary studies by our team indicate that melanomas are highly addicted to TERT, as depletion or inhibition of TERT causes striking and rapid apoptosis. These data support the hy- pothesis that TERT plays a critical role in melanoma and constitutes a compelling target for therapy. The goal of this proposal is to establish the efficacy of targeting TERT in melanoma, alone and in combination with other promising therapies. A corollary of this goal is to dissect the contribution of TERT to melanoma sur- vival and progression. In Aim 1, we propose to systematically dissect the contribution of TERT?s telomere- dependent and -independent roles for melanoma progression and survival, with particular focus on NRAS- mutant melanoma, which is in urgent need of new therapies. To date no group has systematically explored TERT inhibition in melanoma pre-clinical and patient-derived xenograft models, particularly in combination with other therapies. In Aim 2 we will address this gap in knowledge by assessing the efficacy of combining novel TERT-based approaches with promising anti-melanoma therapies, including inhibitors of mitochondrial me- tabolism and immunotherapies. We expect that the proposed work will enable us to: i) Mechanistically deter- mine the contribution of telomere-dependent and telomere-independent functions of TERT in melanoma; ii) Develop novel combination strategies for NRAS mutant melanoma and melanomas resistant to therapy; iii) Provide actionable information that will guide the design of novel, TERT-based combination therapies aimed at preventing and overcoming drug resistance, and enhancing the durability of responses and survival benefits for melanoma patients. Additionally, we expect that our studies will pave the way for novel treatments for other cancers with TERT and/or RAS mutations, heightening the potential impact of our proposal.